The proposed research will examine the tendency of female mosquitoes to refrain from host-seeking during and after the development of oocytes. Our recent data show that this host-seeking inhibition results from a hemolymph-borne factor. This investigation will attempt to localize the site of inhibitor production and also examine the influence of insemination, and hormones associated with oocyte development, on the host-response, using techniques of hemolymph transfusion and organ transplant. Our criterion for the presence of host-seeking behavior is the performance of mosquitoes in an olfactometer.